This invention relates generally to power supply systems and more particularly to overvoltage detection apparatus for use in controlled inverter type power supplies for providing uninterrupted power to an electrical load.
Frequently, power supplies are used in critical environments where it is essential that the electrical load being driven by a power supply inverter cannot be interrupted or shut down for any length of time. Further, the load must be protected from overvoltage. To gain reliability it is customary to connect the outputs of two or more power supplies in parallel whereby they supply a common voltage to the load. One power supply serves as a backup for the other in the event one of the supplies develops a malfunction and has to be turned off.
In prior art systems, to minimize interruption of the power supplied to the electrical load and to prevent damage in the event of a power supply failure, (overvoltage at its output) a crowbar or shorting circuit is usually employed. Each power supply has a crowbar circuit connected to its inverter output to sense the output voltage. When that voltage exceeds a specified level the circuit is activated to immediately short out the output of the inverter. The main disadvantage of the crowbar scheme, even though it protects the load and the power supplies, is that, in a parallel system the crowbar circuit is activated in all of the supplies when the output voltage exceeds the specified level. This is due to the fact that each crowbar circuit senses the common voltage. As a result the voltage to the load is interrupted until the power supply causing the overvoltage can be either physically turned off or removed and the other supply(s) placed back on line.
In view of the preceeding disadvantages it is desirable to provide means in the power supplies of a paralleled power supply system which eliminates interruption of the common voltage supplied to an electrical load when one of the power supplies generates an overvoltage at its output.